You realize that the person is still male and is still the children's father irrespective of any attempt to change his secondary sexual appearance, lifestyle, and behavior? A person can't change his/her sex. It's embedded in the chromosomes of each of the billions of cells that compose the person.

I'd leave the person's sex and relationship to the children alone (since they haven't changed) and handle the transgender part of his life with a custom tag.

This issue has been discussed before. This recurring issue is about using a genealogy program, whose purpose is to document genetic relationships, but then trying to document family/social relationships. TMG assumes, and enforces, the Primary "parents" of a child being one male and one female and the program is designed to assume it is a genetic relationship.

See especially the discussion here about Same Sex couples. As I mentioned there, I recommend creating two separate "people" in the TMG database, one person before the change and one after. For details see that topic and also my discussion of two approaches to recording Adoption data in my on-line book here.

David, I now notice that you were the person who asked this same question in that other post I referenced, which I answered over a year ago. Was there something about that response of mine, or the discussion in my book, which you did not understand?

Describe what you find confusing and I will try to explain in more detail.